1. Field
Apparatuses and methods consistent with the exemplary embodiments relate to a structure of a battery pack containing a plurality of battery modules each of which includes a plurality of cylindrical batteries.
2. Description of Related Art
Battery packs configured by housing battery sets including a number of batteries connected to one another in series or in parallel in casings are used in electric motor vehicles or the like. Such battery packs cause problems, such as decrease in output thereof and decrease in recharging capacity, if the temperature becomes lower. There has been a conventional proposal to provide a battery pack with a heater so as to heat each battery by this heater if the temperature is low.
For example, Japanese Patent No. 5392407 discloses a technique regarding a battery back including plural cylindrical batteries and a metallic battery holder that holds the plural cylindrical batteries wherein a heater is directly disposed to a side surface of the battery holder so as to heat the cylindrical batteries through the battery holder.
Japanese Patent Application Publication No. 2012-243535 discloses a technique regarding a battery pack including plural cylindrical batteries and a battery holder partitioned into separated battery housing spaces in each of which each of the plural cylindrical batteries can be housed wherein a heating element is disposed with a heating surface thereof in contact with part of an outer circumferential surface of each cylindrical battery so as to directly heat the part of each cylindrical battery by the heating element.
Japanese Patent Application Publication No. 2008-053149 discloses a battery pack including: a stacked battery formed by stacking plural square batteries; a casing that houses the stacked battery and has a separator providing separation from the stacked battery; and a heater disposed to an outer surface of the separator, wherein the stacking battery is configured to heat each square battery through air present between the separator and the batteries.
Recently, a longer travel distance has been required in electric vehicles. A longer electrically-driven travel distance has also been required in hybrid vehicles. More batteries are required to be installed on a vehicle in order to increase an electrically-driven travel distance, but a space in the vehicle for allowing installation of the batteries is limited. For this reason, it has been considered to mount a number of battery modules in a relatively small size in a casing adjusted to a vehicle space.
As aforementioned, if a number of battery modules are mounted in a battery pack, a number of heaters are required, which causes a problem that complicates a structure, wiring, or the like. Such a problem might be caused in both the case of heating the batteries by the heater directly fixed to the battery holder as described in the related art of JP 5392407B, and the case of attaching the heater in contact with each cylindrical battery so as to heat each cylindrical battery as described in the related art of JP 2012-243535 A. In the related art of JP 2008-053149 A, an air space projecting from the casing is provided and the heater is attached to the outside of this air space; therefore, a dimension of the battery pack becomes greater, which might make it difficult to house the battery pack in a vehicle space in some cases.